This invention relates to a deviation calculation rule used to provide a direct reading of all the necessary parameters and variables for monitoring the drilling path of deviated holes developed in a two dimensional geometric area thereby eliminating the traditional calculations that are done today using modem means of calculation, mainly computers.
Before going into detail about the deviation calculation rule, we will explain what two dimensional (2D) deviated holes are and will define the parameters and concepts the users of this rule will have to use.
In the early stages of oil drilling, wells were mostly vertical. Improvements in drilling techniques, the deepening of the pools, the discovery of new off shore oil fields and the cost of xe2x80x9coffshorexe2x80x9d infrastructures soon made it necessary to implement and improve techniques called deviation techniques. The deviation of a well consists in moving the path of a well away from the vertical line that passes through the wellhead, using a technique adapted thereto. The bottom of the well can therefore be moved by a certain lateral distance (that could be several km) in relation to the vertical line that passes through the wellhead. It then becomes possible to drill a greater number of wells whose paths are divergent from one same above-ground or offshore structure (xe2x80x9cclusterxe2x80x9d on land, offshore drilling rig or underwater xe2x80x9cclusterxe2x80x9d). These wells drain the oil from a relatively wide reservoir area compared to the space needed on the surface or at the bottom of the sea to exploit it.
Thus over the last fifty years, we have seen development taking place in a whole typology of deviated wells, among which we can name J wells, S wells, more or less complex horizontal wells, long deflection wells, multiple target wells, multi-lateral wells
Whatever the degree of sophistication of these wells, they all have more or less complex paths that must be located in the space. There are two main classes of paths: two-dimensional paths and three-dimensional paths.
The difference between these two classes of paths is based on the manner in which the inclination and the azimuth move over most of the path. We remind you that the inclination at a given point of a path is the angle that is created, in a vertical plane, by the tangent to the path at this point and the vertical line that passes at this point and that the azimuth of the path at this point is the angle created between the vertical plane that contains the tangent to the path at this point and the geographical vertical plane of reference.
In a 2D path, the variations of the inclination over most of the sections of the well are usually very large compared to the variations of the azimuth. This means that the well remains, for the most part, in the same vertical plane. However, if the variations of the inclination and the azimuth came closer together in absolute values, the inclination and the azimuth would have to progress in completely separate ways, meaning one after the other but never at the same time if the path is to remain 2D.
In a 3D path, the variations of the inclination and the azimuth over most of the sections of the well are much closer in absolute values than in the 2D path. Over substantial portions of the well, the inclination and the azimuth move together in significant way.
This differentiation between the 2D and 3D paths is crucial because the deviation calculation rule that is the object of this invention is only used in cases involving 2D paths. We must however note that this field covers most of the paths that are drilled today.
There are four different types of sections that constitute 2D paths:
vertical sections in which the value of the inclination is low and close to zero and in which the well""s path moves very little laterally, in relation to the vertical line that passes through the wellhead;
curved sections in which the value of the inclination may or may not start at zero and changes significantly compared to the value of the azimuth and in which the path of the well moves laterally in relation to the vertical line that passes through the wellhead in a given direction. These lateral movements generally tend to move the path of the well away from the vertical line that passes through the wellhead, but the opposite is possible and relates precisely to the case of xe2x80x9creverse curvedxe2x80x9d wells. Among the curved sections, we note positive curved sections in which the value of the inclination increases along the path and negative curved sections in which the value of the inclination decreases along the path. The curved sections may have a constant (arc of circle sections) or variable (catenary sections) curve radius;
straight sections in which the inclination remains constant and equal to a given non null value and in which the path moves laterally in relation to the vertical line that passes through the wellhead in a given direction. As with the curved sections, the straight sections can move the path of the well away from to closer to the vertical line that passes through the wellhead;
sections called navigation or pilot sections, specifically adjusted to the drilling of horizontal drains, in which the inclination changes a lot and tends to follow the dip of the geological beds, in sections, with areas called transition areas; in these sections, the inclination values of the path oscillate around the horizontal position (+ or xe2x88x9290xc2x0 inclination, in a wide range from 70xc2x0 to 120xc2x0); they consist of successions of curved sections and straight sections.
In order to plan and monitor the 2D paths, they must be located in a two-dimensional space, meaning in a plane that, theoretically, consists of the vertical plane that contains the path. As shown in the enclosed FIG. 1, this plane P can be located in a local reference system through its azimuth a, the angle created by the plane P and a vertical reference plane P1 that contains a fixed geographical landmark located on the surface. The path T, even a 2D type path, rarely develops in a single plane because it presents slight variations of the azimuth. This is why, for the monitoring of the path and the calculations related to it, we will choose as plane P a projection plane on which the path will be projected and this is also why, for the use of the deviation calculation rule, we will consider that the azimuth of the well remains mostly constant, which is an acceptable approximation.
Path T of the well is only known through deviation measurements that are carried out at certain points along the path, in general every drilled 30 m or in certain more critical cases, every drilled 10 m. In the purely 2D field, these are inclination measurements that are linked to drilled lengths in which the drilled lengths correspond for the most part to the cumulated length of the drill rods that are used to drill the well. The drill path is built through calculation, in sections, from these measurement points. In the purely 2D field, we graphically build the path by joining the successive points of measurement M1, M2 . . . with two types of curves: straight sections when the measurement of the inclination remains unchanged between the points of measurement, and arcs of circle when the measurement of the inclination has changed between the two points, whether upward or downward.
The plane P is defined by two orthogonal axes: a horizontal axis directed in the azimuth of the well path and a vertical axis directed downward. On the horizontal axis, for each deviation measurement, we note the cumulated horizontal deflection values DEP of the well, in relation to a geographic referential that can be the geographic position of the wellhead I. The reference is not necessarily the wellhead, it can also be the center of a rig, or any other point that serves as a common reference for a group of wells. For directional calculations we usually work in a local reference and make the origin of the axis coincide with the wellhead.
On the vertical axis, for each deviation measurement, we note the cumulated vertical depth values PV of the well, in relation to the topographic referential that can be the location of the wellhead. For directional calculations, we work with a local reference and make the origin of this axis coincide with a location that is accessible on the floor of the drilling device through which pass the drill rods that will constitute the string and whose cumulated measurement will make it possible to establish the drilled length.
In theory, this system of coordinates is sufficient to be able to locate the path point by point. On the other hand, the DEP and PV variables cannot be measured directly; they are obtained through calculations that require the knowledge of a number of elements (deviation measurements) and we must formulate a certain number of hypotheses (method of calculation and construction of the path) which we will address below.
Given that the curved section (arc of circle) involves the largest number of parameters, it is the one we will use in what follows in order to emphasize the various variables that make it possible to locate the path in space. The attached FIG. 2 represents a portion of the projection plane P that contains an arc of circle section A demarcated by an entry point E and an exit point S.
The DEP and PV variables are calculated using the following three parameters: the inclination i1 measured at the point of entry E, the inclination i2 measured at the point of exit S and the drilled length xcex94LF between the point of entry and the exit point. A simple geometric calculation involving the bend radius R of the arc of circle section makes it possible to determine the horizontal deflection deviation xcex94DEP and the vertical depth deviation xcex94PV between points E and S of the arc of circle section being considered. These deviations (relative) are added or subtracted, depending on the case, from the previous accumulations in order to obtain the DEP and PV variables (absolutes) at a given point of the drilling path.
The values of these two variables are provided by the following formulas:
xcex94PV=180/xcfx80xc2x7xcex94Lf/(i2xe2x88x92i1)xc2x7(sin i2xe2x88x92sin i1)xe2x80x83xe2x80x83(1)
xcex94DEP=180/xcfx80xc2x7xcex94LF/(i2xe2x88x92i1)xc2x7(cos i1xe2x88x92cos i2)xe2x80x83xe2x80x83(2)
where i1 and i2 are expressed in degrees.
The main hypothesis that is made in the calculation of these variables is that the curved section is comparable to an arc of circle and therefore has a constant bend radius that is equal to the radius R of the arc or circle. The quantity xcex94LF/(i2xe2x88x92i1) that appears in formulas (1) and (2) is precisely equal to the radius R1 when (i2xe2x88x92i1is expressed in radians. The 180/xcfx80 factor is a conversion factor that makes it possible to express (i2xe2x88x92i1) in degrees.
We will note that the bend radius R is rarely used by drillers. They prefer the notion of xe2x80x9cbuild-upxe2x80x9d gradient (Gbu) which is the variation of the inclination over a given drilled length. This variation is positive when the value of the inclination increases over the section, and negative when it decreases. In this case where we compared the curve section between the two designed points to an arc of circle, the Gbu is of course considered as constant along this section.
There are three distinct fields of application for the above-mentioned deviation calculations: planning of wells, monitoring the path and helping to make decisions using xe2x80x9cblankxe2x80x9d calculations and investigations around piloting hypotheses linked to the path of the well.
Planning the wells consists in building the theoretical path or the deviation plane. Yet in this area, the calculations are more complex essentially because of the accession of the horizontal wells. Indeed the paths are much harder to plan when we have to follow the geological beds governed by the laws of nature (case of the horizontal drains) than when passing through them locally, over a certain length (case of classic deviated wells).
Monitoring the path is essentially used to locate the drilled path and compare it directly to the theoretical curve that resulted from the planning. The calculations are done for each point of measurement. If in the case of classic deviated wells the deviation plane is followed to the letter, at least as far as its final objective of passing through the target is concerned, it is not so for most horizontal wells as the drain is piloted to follow the geological beds, with the result that the deviation plane quickly becomes obsolete and a systematic re-planning must take place during the acquisition of each new measurement.
The xe2x80x9cblankxe2x80x9d calculations and piloting scenarios are areas where the sum of the calculation has increased the most with the accession of the horizontal wells. The re-planning of the well with each new deviation measurement requires testing a certain number of hypotheses in order to be able to make the right decisions that pertain directly to the piloting of the drain hole. Furthermore, the overall improvement of drilling techniques and in particular of the transmission of deviation data in real time, has greatly complicated the job of the operator by reducing the reaction times.
We will note that for the planning and following of the path, all calculations must be done in absolute, meaning that the distances are cumulated in order to be able to locate the path in space, whereas repetitive xe2x80x9cblankxe2x80x9d calculations are relative, because what the operator is seeking in this case, are the variations of one or the other variable from a known starting point and under the influence of one or more parameters.
The afore-mentioned calculations cannot be ignored and are necessary to monitor and execute deviated or horizontal drillings. In the early days of deviated drilling, these calculations were done by hand or with the help of a calculator. Today, they are done either using a programmable calculator or a PC. However, these modem means of calculation do have a certain number of drawbacks:
the safety rules relating to the risks of deflagration on the rig floor prohibit the use of a PC at this location. Therefore the PC must be kept away from the rig floor which is an important center of decision making since it is where the deviation measurements arrive first and foremost and where the path corrections will be applied.
to solve a problem linked to the well path, the data are entered in the computer in the form of a series of numbers and in return, the solution is also offered by the computer in the form of a series of numbers. Yet the problem is geometric, and these series of numbers, obtained without any particular thinking challenge, do not sufficiently take into account the physical reality. Add to that fatigue and the operator could easily confuse the values or forget a sign that could be crucial;
xe2x80x9cblankxe2x80x9d calculations, or some of them, have the added particularity of being performed in a repetitive mode, meaning that they only lead to the solution of the problem after trial and error. These repeated calculations are often very tedious;
entering the data on the keyboard of the PC or programmable calculator quickly becomes a serious handicap on a work site since the operator does not always have clean hands and furthermore he may not have the necessary concentration to correctly type the problem""s data on the small keys the first time around;
computers are sensitive and fragile devices and they are subjected to the difficult conditions encountered on the sites, such as dust, sand, a more or less stable and filtered electric supply current. Furthermore, as they are not connected to the network, they must use a diskette to move data from one computer to another which is not a safe means of communication as the diskette may transmit a certain number of more or less aggressive viruses. Also, in such a context, computer failures cannot be excluded;
the software used for directional monitoring is usually of the xe2x80x9cmulti-windowsxe2x80x9d type where one must open and close a certain number of windows before entering the data to a simple problem; these repeated operations easily become tiring after a while;
even if computers are becoming a widely used technique, it is not always a unanimous decision to use them among some of the men on the site.
The object of this invention is to remedy the above-mentioned drawbacks linked to computers and programmable calculators and, with this in mind, it proposes to replace them with a calculation rule that can determine the various variables of directional drilling during the path monitoring and decision making stages. Of course, the rule offers the usual advantages peculiar to all calculation rules, namely:
it can be used anywhere on the site, without any restrictions as to the area;
it is operational as soon as it is taken out of its case;
the calculations from the rule are performed in relative form, where knowledge of the well""s history and path are not necessary for the rule to be immediately operational;
no specific knowledge is required to use it and it represents the physical sizes handled by the user in more practical terms;
it is not subject to any risk of failure, to which are added other advantages that will become apparent in the following pages.
Therefore, this invention relates to a deviation calculation rule of the circular type for the monitoring of a two-dimensional deviated well path, where this rule is characterized by the fact that is consists of:
a support plate on which is marked a fixed circular dial used to locate or index the angle of inclination at the entry point of a section of the path and the angle of inclination at the exit point of said section, where said fixed dial has two semi-circular scales each graduated counter clockwise from 0 to 180xc2x0 and whose common extremities are located on a diametral line of said dial, where the first scale represents the range of increase of the inclination when dealing with the problems linked to sections with positive curves and the second scale represents the range of decrease of the inclination when dealing with the problems linked to sections with negative curves.
at least two interchangeable rotary disks used for indexing the entry inclination, choosing or locating the xe2x80x9cbuild-upxe2x80x9d gradient value and choosing or reading the drilled length on the interval being considered, where said rotary disks have a diameter that is slightly less than that of the circular dial and are stacked on the support plate concentrically to the dial in such a fashion that only the disk that is placed on the top is active and the other is kept on stand-by waiting to be used, where said rotary disks have a plurality of concentric circles each corresponding to an inclination gradient for a given drilled length (Gbu), so that the set of disks covers all the gradient values that are commonly found in practice, where each disk is divided by a diametral line that is used to locate and index the entry inclination value of said section on the scales of the circular dial marked on the plate, and that demarcates, on each of said concentric circles, a first semi-circular scale that is graduated counter clockwise in drilled lengths and makes it possible to work in the range of increase of the inclination and a second semi-circular scale graduated in the same way except clockwise, that makes it possible to work in the range of decrease area of the inclination, where the zero graduation of both these semi-circular scales coincide.
at least one rotary bi-sectoral disk used for reading or indexing an exit inclination, or locating the xe2x80x9cbuild-upxe2x80x9d gradient value and managing the path calculations linked to the straight sections, where said bi-sectoral disk has the shape of two circular sectors diametrically opposed at their top, whose radius is less than that of the circular dial and is arranged above the rotary disks, concentrically to the latter, where one of the sectors of the bi-sectoral disk has a first graduated scale used to locate the Gbu circles of the active upper rotary disk on one of its radial edges, and a second scale used to locate the Gbu circles of the other rotary disk waiting to be used on the other radial edge, where said scales meet symmetrically on the radial edges of the other sector, and where said bi-sectoral disk also has a diametral line on each side of which are marked two scales head to tail, graduated in drilled lengths and used to deal with problems linked to straight lines, where said bi-sectoral disk and the rotary disks can be turned independently of each other, around a link element, such as an axis, that passes through them in their center and also passes through the support plate at the center of the circular dial,
and adjustable sliding means that allow for either a simple reading, or the pre-selection of the deflection deviation or the vertical depth deviation at a given value, so as to determine the Gbu circle that corresponds to this deviation and read the drilled length on this circle, based on the entry and exit inclination values that correspond to the problem of the path in question.
According to a first mode of execution of the invention, said adjustable sliding rules include:
a first sliding system that consists of a straight slide track mounted in a sliding manner on the support plate, entirely outside the circular dial, a fixed rule and a mobile rule both perpendicular to the slide track and extending on the side of the circular dial, where the fixed rule is attached by one of its extremities to the track, whereas the mobile rule has one extremity that is mounted in a sliding manner in the slide track, a scale marked lengthwise on the slide track and whose zero coincides with the inside edge of the fixed rule;
and a second sliding system identical to the first sliding system, located outside the circular dial and extending perpendicularly to the first sliding system.
According to a second mode of execution whose object is to simplify the manufacture of the rule, said adjustable sliding means consist of:
a small rule mounted on the support plate parallel to the 0-180xc2x0 diametral line of the circular dial and that can slide in a direction that is perpendicular to its own direction while covering the entire surface of the support plate.
a sliding element in the shape of a rectangular dial, also mounted on the support plate and of which one of the sides is assembled in a sliding manner to said small rule, in such a way that said dial shaped element can slide along said small rule parallel to said diametral line, where the four sides of the dial shaped element each have a graduated scale on their inside edge,
and four cursors respectively mounted in a sliding manner on said sides of the dial shaped element so as to locate a particular chosen graduation on said graduated scales in order to pre-select values.
The invention will now be described in detail using the attached drawings where: